Today, sensors are applied in numerous applications, such as, for example, automotive applications. Safety critical applications, such as Anti-Blocking Systems (ABS) or Electrical Power Steering (EPS), for example, often rely on redundant sensor concepts to achieve sufficiently low probabilities of random hardware failures. Such redundant sensor concepts may use dual-sensor solutions with two redundant sensors instead of one. Dual-sensor packages may integrate two sensors with respective separate power supplies and separate signal outputs. The sensors are electrically independent due to galvanic isolation. This means that the two sensors work independently, thereby increasing system reliability.
In particular, integrated magneto-resistive sensors are predestinate for this kind of redundancy since they are small and can be located over circuitry. Magneto-resistive sensors can include Giant Magneto-Resistive (GMR), Tunnel Magneto-Resistive (TMR), Anisotropic Magneto Resistive (AMR) and other well-known magneto-resistive technologies, referred to collectively as XMR technologies. Furthermore XMR support the integration of electrically independent sensors on a single chip, since the du not use the silicon bulk and are thus galvanically isolated by isolators like oxides or nitrides.
Redundant sensor concepts require sufficient independency of the redundant sensor elements. A reason for dependent faults affecting either one or the other sensor may be a shortcut or leakage through isolation layers between the two magneto-resistive sensors which may, for example, be supported by defects or contamination that reduces the isolation capability of the used separation or insulation material, for example, oxide or nitride. Such defects do often not lead to safety critical leakage immediately, but may be activated during operation after some time in an electrical field.
One way to reduce the probability of shortcuts or leakage through separation or insulation layers could be to increase the distance between the adjacent sensors. However, this would be costly since the area between the magneto-resistive structures would be comparable or even larger than the magneto-resistive elements themselves.
Thus, there is a need for improved concepts for reducing the probability of shortcuts or leakage between magneto-resistive sensors of redundant sensor Integrated Circuits (ICs).